The signaling processes that divides the anterior-posterior (A-P) axis of the vertebrate nervous system into regional identities not well understood. This patterning is in part dependent on the organizer, which induces ectoderm to form neural tissues during gastrulation. It is known that signals from other regions of the embryo also have a role in eliciting patterned neural identity, and that a degree of A-P neural patterning can still occur when the organizer is surgically or genetically ablated. It is therefore of interest to determine the degree of patterning that can occur when formation of earlier dorsal signaling centers is impaired. We have discovered a zebrafish maternal effect mutant, ichabod, which is characterized by the failure to form a functional organizer. Mutants do not properly localize B-catenin in dorsal yolk syncytial layer (YSL) or blastoderm margin nuclei, resulting in the absence or very low levels of B-catenin-mediated signaling. Mutant embryos are severely affected in A-P development, exhibiting a graded series of anterior truncations, which in the most severe cases result in a complete absences of head and trunk. In this proposal, we employ ichabod and other zebrafish mutant embryos to discover genes essential for formation of neurectoderm of different A-P identities, and to gain insight into the mechanisms that control this pattern. (1) We plan to better characterize the A-P pattern of neural development in ichabod embryos, to determine the extent of fate changes and apoptosis in the neurectoderm, and to study the interaction of BMP and B-catenin-mediated pathways in neural development. (2) We plan to use differential hybridization screening of arrayed cDNA libraries to identify and isolate those genes that are expressed in wildtype embryos, but are either inactive in ichabod embryos. The goal is to discover genes that are required for proper A-P neural tube formation that are not expressed when the YSL and organizer signaling is impaired (to be carried out collaboratively with Dr. David Grunwald of the University of Utah). (3) We plan to clone and molecularly characterize the ichabod locus. The ichabod gene product may have a novel role in controling nuclear localization of B-catenin without having effects on B-catenin stability. Molecular characterization of this gene would enhance our understanding of the Wnt-B-catenin signaling pathway and further clarify the network of gene interactions that results in proper neural development.